1. Field of the Invention
The invention pertains to a fiber-based product comprising carboxymethyl cellulose, carboxymethylated hemicellulose and carboxymethylated starch. The fiber-based product is obtained by simultaneously performing alkali extraction of hydrocolloid from the fiber and carboxymethylation, with a carboxymethylating agent, thereby converting extracted cellulose to carboxymethyl cellulose and also carboxymethylating some extracted hemicellulose and starch. The fiber-based product may be used in adhesives, such as corrugating adhesives and laminating adhesives as well as other applications. The invention also concerns adhesives comprising the fiber-based product.
2. The Prior Art
Carboxymethyl cellulose is usually prepared by etherifying cellulose with alkyl monochloracetates. For example, U.S. Pat. No. 4,526,961 describes a method for preparing water-soluble carboxymethyl cellulose comprising the steps of alkalizing cellulose to produce alkali cellulose and then etherifying the alkali cellulose with an etherifying mixture having alkyl monochloroactetate in the presence of an organic solvent. The carboxymethyl cellulose is generally obtained from “clean” cellulose feedstock and thus there are minimal, if any, other carboxylated materials in the carboxymethyl cellulose.
Starch-based products, such as adhesives, may contain carboxymethyl cellulose. For example, U.S. Pat. No. 4,272,295 discloses a starch-based adhesive comprising a lypophilic colloid, which may be carboxymethyl cellulose among others, and partially gelatinized starch. U.S. Pat. No. 5,503,668 discusses the replacement of some or all of the starch component of a corrugating adhesive with solubilized fiber and addresses that an optional carbohydrate component can be added. Carboxymethyl cellulose is listed among a number of materials as a carbohydrate component of the adhesive described in U.S. Pat. No. 5,503,668, and modified starch is disclosed as the preferred carbohydrate for the adhesive formulation of U.S. Pat. No. 5,503,668.
Adhesives are used in a variety of industries and trades to bond substances together. Adhesives are used for laminating materials, e.g. bonding pieces of material together to form a structural unit like in the furniture industry where a layer of decorative material may be bonded to wood. Adhesives also have an important role in the corrugating industry.
In the corrugating process, adhesive is commonly applied to the tips of the flutes of a corrugated medium. Then a non-corrugated flat paper liner is applied against the adhesive coated flutes as they pass between a corrugating roll and a pressure roll. The resulting product has the corrugating medium on one side and a flat liner on the other side and is called a single-face portion. The single-face portion may be used “as is” (called a “single-face” board) or adhesive may be applied to the flute tips of the single-face portion and a second flat sheet can be applied in the same manner as the first in what is called a “double-face” or a “double-back” operation. The second liner sheet is treated with heat and reduced pressure (relative to the pressure used to make a single-face portion) immediately following contact with the adhesive coated flutes as they pass between a corrugating roll and a pressure roll.
Starch-based adhesives, which can be of the carrier, no-carrier and carrier no-carrier type, are commonly used in processes for manufacturing corrugated paper board. In carrier type adhesives, a portion of the starch (or dextrin) forms a carrier, often known as the gelatinized phase, which suspends the balance of the starch which is in an ungelatinized state. Under conditions of heat and pressure, the ungelatinized starch is rapidly hydrated and gelatinized to increase quickly the viscosity and adhesivity of the adhesive composition. In no-carrier type adhesives, all of the starch is slightly cooked or swollen with heat and caustic soda for viscosity. Finally, carrier no-carrier type adhesives have a portion of the starch which forms a carrier and is responsible for about one half of the viscosity and the remaining viscosity is obtained by slightly swelling the uncooked starch.
Starch based corrugating adhesives of the carrier, no-carrier and carrier no-carrier type comprising added hemicellulose are described U.S. Pat. No. 5,358,559. Adhesive compositions where the hemicellulose is extracted from corn fiber in situ during the process of preparing the carrier phase are discussed in U.S. Pat. No. 6,368,443 B1.
We have discovered that extracting hemicellulose by either dry or wet reaction with alkali with simultaneous carboxymethylation results in the carboxymethylation of extracted cellulose, hemicellulose and fiber. The resulting fiber-based product comprises hemicellulose, carboxymethyl cellulose (same or all of which is in the form of a carboxymethylated hemicellulose-cellulose complex), carboxymethylated hemicellulose and carboxymethylated starch. Adding purified carboxymethyl cellulose to an adhesive does not result in an adhesive having other carboxymethylated components (e.g. carboxymethylated hemicellulose and carboxymethlated starch).
We have further discovered that adhesives comprising the fiber-based product have improved bonding properties. Cellulose from the hemicellulose extraction acts as a diluent in adhesive under high shear conditions which negatively affects the bonding properties of adhesive. The fiber-based product from the simultaneous alkali extraction and carboxymethylation, or the simultaneous alkali extraction and carboxymethylation when making adhesive, results in carboxymethylated components that contribute tack and viscosity to the adhesive which improves bonding. Also, the fiber-based product in the corrugating adhesive will eliminate, or reduce, the amount of boron containing compounds needed for the adhesive.
In the present Specification all parts and percentages are on a weight by weight basis based on the total amount of components in a composition of matter, unless otherwise specified. The term “by weight of solids” means the weight percent of the component based on the total weight of solid material in the composition of matter.